Not Applicable
This invention relates to arrangements for securing the roof of a structure against damage caused by high winds, earthquakes, and the like.
It is known to reinforce a building wall to resist wind and earthquake damage by the use of what will hereinafter be called a xe2x80x9ctop plate tie downxe2x80x9d arrangement in which vertically disposed elongate fastening members that can be loaded in tension (e.g., a threaded metal rod) connect a top plate of the protected wall to an anchor beneath the wall, where the anchor is fixedly attached to a slab or is buried in or otherwise attached to the ground. As described in a parent application now issued as U.S. Pat. No. 6,161,339, a satisfactory anchor for such apparatus may be set in position prior to pouring a concrete foundation slab. The anchor can then be used both to retain a sill plate and to connect an elongate top-plate fastener to the foundation.
The use of conventional embedded anchors can lead to problems in installing a top plate tie down system if the anchors are not embedded at the proper positions along a sill or if the anchors are not set in a fully upright position. Because it is difficult to ensure that a correctly oriented anchor is located at each position where a top plate elongate fastener is to be installed, many builders would prefer to fasten anchors to an already hardened slab.
It is known, for example, to anchor a sill plate to a slab by driving through the sill plate into the slab and then gluing (e.g., with an epoxy cement) an anchor into the hole formed in the slab. If dust from the drilling operation is not carefully removed from the hole before inserting an epoxy-enrobed anchor, this approach results in an anchor with a very low pull-out strength. Although such an anchor may be satisfactory for retaining a sill plate against lateral forces, it can not safely be used as part of a top plate tie down apparatus. Glued, or otherwise bonded, anchors are generally not acceptable for top plate tie down use because of both the high likelihood of there being at least one dust-contaminated and weakened anchor along a wall, and because of the time and expense involved in running a separate pull-out test on each anchor.
Expansion-type anchors are widely used when a high pull-out strength connection must be made to a masonry support. Because this sort of anchor induces a high lateral stress in the masonry, it can cause portions of a masonry body to spall off if the anchor is placed too near a free edge of the body. Top plate tie-down arrangements are, of course, installed on exterior walls near the edge of a foundation slab. Hence, expansion anchors can not be used.
Self-tapping threaded masonry anchors are of interest to the present invention. Notable among commercially available hardware of this sort products sold under the trade name xe2x80x9cWedge-Boltxe2x80x9d by Powers Fasteners, Inc., of New Rochelle, N.Y. Patent references in this technical area include:
U.S. Pat. No. 5,674,035, wherein Hettich et al. teach a thread forming screw having ratios of the sizes of various portions of the screw selected to reduce screw-in torque;
U.S. Pat. No. 5,531,553, wherein Bickford describes a masonry anchor having a dust-relief groove disposed between thread lands; and
U.S. Pat. No. 4,439,077, wherein Godsted discloses a threaded fastener for use in hard aggregates.
The invention provides an improved anchor for a top plate tie down arrangement comprising a plurality of elongate vertical fasteners attached between the top plate and respective anchors disposed beneath the wall. In a preferred embodiment the anchor comprises a stud having one end adapted to be threaded into a concrete foundation slab and a second end threaded to receive a coupling nut for attaching the stud to a respective elongate vertical fastener.
It is an object of the invention to provide a top plate tie down apparatus connecting a top plate of a wall to a concrete foundation. As is conventional in construction practice, the wall extends upward from a sill plate placed on the concrete foundation and having a plurality of generally vertical throughholes through it, where the throughholes can be formed either before or after placement of the sill plate on the sill. The inventive apparatus preferably comprises a selected number of anchors, where the number of anchors is generally selected to match the number of throughholes in the sill. Each of these anchors has a respective portion threadably engaging the foundation beneath the wall along an embedment length of the anchor, each anchor has a respective upper portion threaded along at least a selected penetration length that is selected to accord with the accessible threaded depth of a connecting nut, and each of the anchors has a length equal to a sum of the penetration length, the sill thickness and the embedment length. In addition, the preferred apparatus comprises the selected number of vertical tensile fasteners, where each of the vertical tensile fasteners is connected to the top platexe2x80x94e.g., by means such as those shown in the parent application hereto. Each of these vertical tensile fasteners further comprises a respective lower threaded portion at a respective lower end thereof, where each of the lower threaded portions has a selected lower portion thread length that, like the thread length on the anchor, is selected to accord with a connecting nut Each of the connecting nuts has a length at least as large as the sum of the penetration length and the selected lower portion thread length and has a first end threaded onto a respective one of the anchors, and a second end threaded onto the respective lower threaded portion of a respective one of the vertical tensile fasteners.
It is an additional object of the invention to provide a method of attaching a top plate of a wall to a slab disposed beneath the wall. The preferred method begins with a step of drilling a selected number of holes into the slab, where each of the holes extends into the slab by more than an embedment length of an anchor bolt, and preferably by about one bolt diameter more than the embedment length. An anchor bolt is then inserted through a throughhole in a sill plate into each of these holes and turned so as to thread the anchor bolt into the hole. In the preferred method a connecting nut threaded onto an upper threaded portion of each anchor bolt provides a set of flat surfaces that can be gripped by a wrench and used to turn the bolt into the hole. Moreover, it is also preferred to place a washer between the connecting nut and the sill plate before turning the bolt into the hole so as to effectively capture the sill plate between the connecting nut and the slab without deforming the sill plate. It will be understood by those skilled in the art that this method can be carried out by the use of a sill plate that has pre-drilled throughholes, or by drilling through the sill plate when drilling the hole into the slab.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.